Rapid growth of the wireless mobile communication market demands various multimedia services in a wireless environment. To provide the multimedia services, as large capacity of transmission data and high speed of the data transfer are under way, researches are conducted on multi-antenna systems for efficiently using the limited frequencies. A representative transmission mode of the multi-antenna system includes a Multiple Input Multiple Output (MIMO) transmission mode.
Using the MIMO transmission, a transmitter and a receiver of a multi-antenna system send and receive signals over a plurality of antennas. Compared to a single antenna system, the MIMO multi-antenna system can raise the transmission reliability and the data rate by using independent channels per antenna without requiring additional frequency or additional transmit power.
As such, the MIMO multi-antenna system can efficiently transmit signals only when the channel independence of the antennas is guaranteed. When the channel independence of the antennas is not guaranteed, the MIMO receiver cannot distinguish the signals received via the antennas and not efficiently carry out the MIMO transmission. For example, in a Line of Sight (LOS) channel environment, the multi-antenna system cannot ensure channel independence between the antennas. As a result, the receiver cannot distinguish the signals received over the antennas and cannot efficiently fulfill the MIMO transmission in the LOS channel environment.